linux-kernel - Re: [PATCH] Fix irqpoll on IA64 (timer interrupt != 0)

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Message-Id: <20070322161545.c8ad3b7a.akpm@linux-foundation.org>
Date:	Thu, 22 Mar 2007 16:15:45 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Bernhard Walle <bwalle@...e.de>
Cc:	linux-ia64@...r.kernel.org, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] Fix irqpoll on IA64 (timer interrupt != 0)

On Fri, 23 Mar 2007 00:04:07 +0100
Bernhard Walle <bwalle@...e.de> wrote:

> * Andrew Morton <akpm@...ux-foundation.org> [2007-03-22 22:09]:
> > On Tue, 20 Mar 2007 16:00:27 +0100
> > Bernhard Walle <bwalle@...e.de> wrote:
> > 
> > > On IA64, the timer interrupt is not (always?) zero as it is on x86 platforms.
> > > Also, the timer interrupt is CPU-local. Two things need to be changed to make
> > > the irqpoll option make also working on IA64:
> > > 
> > >   o Call note_interrupt() also on CPU-local interrupts in __do_IRQ().
> > >   o Set a variable timer_irq to the value of the timer interrupt
> > >     after the timer interrupt has been registered and assigned.
> > > 
> > > That requires changes in Linux-generic files. The default of timer_irq is 0, so
> > > the patch doesn't break i386/x86_64. However, other platforms also may also
> > > have a timer interrupt non-equal to zero, so they can also use the new
> > > set_timer_interrupt() function.
> > 
> > Couple of things..
> > 
> > I think the term 'timer_interrupt' is a bit generic-sounding.  Would it be
> > better to call it irqpoll_interrupt?  After all, some architecture might
> > want to use, umm, the keyboard interrupt to trigger IRQ polling ;)  
> 
> Well, the documentation of irqpoll says that it's called on the timer
> interrupt. But maybe also the documentation should be changed. :)
> 
> > Also, the code presently passes the magic IRQ number into the generic IRQ
> > code.  I wonder if we'd get a more pleasing result if we were to make the
> > generic IRQ code call _out_ to the architecture:
> 
> I think I have a third solution. There's already IRQF_TIMER, and
> that's used and defined in a few architectures already (like Sh), so
> why not simply use that here. Maybe we should introduce IRQF_IRQPOLL,
> but the concept would be the same. If we don't take care of shared
> interrupt handlers (and I think sharing the timer interrupt is a
> _very_ bad idea, are there architectures that do this?), the could
> would look like this (+ the change in __do_IRQ).
> 
> What's your opinion on this approach? Of course, we would have to make
> sure that IRQF_TIMER is defined on _every_ architectures, but that
> would give us the chance to find out each architecture that also has a
> timer interrupt != 0.
> 
> 
> Index: mainline-msi-init/arch/ia64/kernel/time.c
> ===================================================================
> --- mainline-msi-init.orig/arch/ia64/kernel/time.c
> +++ mainline-msi-init/arch/ia64/kernel/time.c
> @@ -235,7 +235,7 @@ ia64_init_itm (void)
>  
>  static struct irqaction timer_irqaction = {
>  	.handler =	timer_interrupt,
> -	.flags =	IRQF_DISABLED,
> +	.flags =	IRQF_DISABLED | IRQF_TIMER,
>  	.name =		"timer"
>  };
>  
> Index: mainline-msi-init/arch/x86_64/kernel/time.c
> ===================================================================
> --- mainline-msi-init.orig/arch/x86_64/kernel/time.c
> +++ mainline-msi-init/arch/x86_64/kernel/time.c
> @@ -320,7 +320,7 @@ void __init stop_timer_interrupt(void)
>  }
>  
>  static struct irqaction irq0 = {
> -	timer_interrupt, IRQF_DISABLED, CPU_MASK_NONE, "timer", NULL, NULL
> +	timer_interrupt, IRQF_DISABLED | IRQF_TIMER, CPU_MASK_NONE, "timer", NULL, NULL
>  };
>  
>  void __init time_init(void)
> Index: mainline-msi-init/kernel/irq/spurious.c
> ===================================================================
> --- mainline-msi-init.orig/kernel/irq/spurious.c
> +++ mainline-msi-init/kernel/irq/spurious.c
> @@ -146,7 +146,7 @@ void note_interrupt(unsigned int irq, st
>  
>  	if (unlikely(irqfixup)) {
>  		/* Don't punish working computers */
> -		if ((irqfixup == 2 && irq == 0) || action_ret == IRQ_NONE) {
> +		if ((irqfixup == 2 && (desc->action->flags & IRQF_TIMER)) || action_ret == IRQ_NONE) {
>  			int ok = misrouted_irq(irq);
>  			if (action_ret == IRQ_NONE)
>  				desc->irqs_unhandled -= ok;

Seems sane.

Or we could add a new flag specifically for this purpose: IRQF_IRQPOLL_IRQ?
-
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